1. Field of the Invention
The present invention relates to a spindle motor and a method of manufacturing thereof and more particularly to a spindle motor for supporting a rotor using open ball bearings and a method of manufacturing thereof.
2. Description of the Related Art
FIG. 5 shows one example of a spindle motor 51 for driving a hard disk drive device (hereinafter referred to as an HDD), more specifically, a shaft fixed spindle motor 51 wherein a shaft 55 is uprightly provided at the center of a base plate 54 and a rotor 53 is rotatably supported by interposing a pair of ball bearings 52 between the shaft 55 and the rotor 53. Further, FIG. 6 shows a shaft rotatable spindle motor 61 for an HDD wherein a substantially cylindrical fixed shaft 66 coaxial with a pivot 65 of a rotor 63 is uprightly provided and the rotor 63 is made to be rotatable by interposing a pair of ball bearings 52 between the fixed shaft 66 and the pivot 65 of the rotor 63. In general, the ball bearings 52 used for the spindle motors 51 and 61 are sealed ball bearings 52 both side surfaces of which are sealed by shields 56 so as to prevent grease from spilling out and also prevent foreign materials from entering as shown in FIGS. 5 and 6. Further, the shields 56 are arranged in grooves 52c consisted in both side surfaces of the ball bearings 52 (outer rings 52a and inner rings 52b) so as to not being protruded from the both side surfaces of the ball bearings 52. As shown in FIGS. 5 and 6, a pair of ball bearings 52 provided in the spindle motors 51 and 61 are disposed at prescribed intervals in the axial direction of the rotors 53 and 63 by interposing annular spacers 57 therebetween.
In recent years price competitions for hardware is intensified, and spindle motors for HDDs described above are not exceptional thereto. However, in the above-described ball bearings 51 and 61, the grooves 52c at both side surfaces of the outer rings 52a and the inner rings 52b are needed to be machined so that not only the cost of the ball bearings but also the one of the spindle motors 51 and 61 are increased accordingly. Then, open bearings without having shields 56 can be one of the choices because its relative cost will be less expensive, but open bearings without shields cannot be filled with grease in its assembly processes of the ball bearings due to the requirement of controlling the amount of grease as well as a pollution prevention before mounting into a machine. Moreover, open bearings are difficult to be maintained because foreign materials may enter the slide surfaces of the bearings before assembling the machine, resulting in numbers of difficulties when applying to the spindle motors 51 and 61.